Adjustable beds of this type have the lying surface adjusted by a corresponding loading and unloading of the head and back support member, thereby utilizing the body of the recumbent individual for tilting this member about the aforementioned axis.
This member, because of the position of the tilting axis, thus can be angularly displaced about the axis by changing the weight distribution of the body of the recumbent person and each change in the balance can result in an angular displacement.
To prevent undesired tilting movements of the head and back support member, it is known to provide this member with a device for fixing the position thereof about the tilting axis.
The fixing device can be effected by a gas spring and a release of the retained position can be effected utilizing a bowden cable or the like, serving an actuating member.
Since relatively high pressures can prevail in such gas springs, they represent a source of danger and thus create a risk factor in the use of such beds.
Furthermore, gas springs are subject to a high degree of wear and have a comparatively short useful life so that relatively frequent replacement is necessary, since replacement, of course, is associated with high cost.
Swiss Patent No. 643,622 provides a bed-like article of furniture which has a plurality of hingedly interconnected parts which are positioned by a motor.
The motor drives a rod whose displacement effects an angular adjustment of the lying surface.
German Patent document-printed application DE-AS No. 1,174,463 provides a bed structure with movable head and foot members which can be raised and lowered via hydraulic cylinders.
It is also known to lock an angularly adjustable head member of a couch in place until a drop bolt with an opening through which a support rod of the head member can engage with play. The head member can thus be held in selected angular positions between two abutments.